Showing papers by "Noriyoshi Ishii published in 2004"

Thermal effects on quark-gluon mixed condensate g μν G μν q> from lattice QCD

Abstract: We present the first study of the thermal effects on the quark-gluon mixed condensate g , which is another chiral order parameter, in SU(3)c lattice QCD with the Kogut-Susskind fermion at the quenched level. Using the lattices at \beta=6.0, 6.1, 6.2 in high statistics, we calculate the mixed condensate as well as the quark condensate in the chiral limit for the temperature 0MeV / is almost independent of the temperature even in the very vicinity of T_c. This result indicates nontrivial similarity in the chiral behaviors of the two different condensates.

MEM Analysis of Glueball Correlators at T>0

Abstract: Maximum Entropy Method (MEM) is applied to glueball correlators at finite temperature constructed by using 5,500–9,900 gauge field configurations generated in SU(3) quenched lattice QCD with the lattice parameter βlat = 2Nc/g2 = 6.25 and the renormalized anisotropy asat = 4. The results support the thermal width broadening of the 0++ glueball near the critical temperature.

Penta-Quark Anti-Decuplet in Anisotropic Lattice QCD

Abstract: The penta-quark(5Q) Theta^+(1540) is studied in anisotropic lattice QCD with renormalized anisotropy a_s/a_t=4 for a high-precision measurement. Both the positive and the negative parity 5Q baryons are studied using a non-NK type interpolating field with I=0 and J=1/2. After the chiral extrapolation, the lowest positive parity state is found at m_{Theta}\simeq 2.25 GeV, which is too heavy to be identified with Theta^+(1540). In the negative parity channel, the lowest energy state is found at m_{Theta}\simeq 1.75 GeV. Although it is rather close to the empirical value, it is considered to be an NK scattering state rather than a localized resonance state.

Possible Hadronic Molecule Lambda(1405) and Thermal Glueballs in SU(3) Lattice QCD

Abstract: We aim to construct quark hadron physics based on QCD. First, using lattice QCD, we study mass spectra of positive-parity and negative-parity baryons in the octet, the decuplet and the singlet representations of the SU(3) flavor. In particular, we consider the lightest negative-parity baryon, the $\Lambda$(1405), which can be an exotic hadron as the $N \bar K$ molecular state or the flavor-singlet three-quark state. We investigate the negative-parity flavor-singlet three-quark state in lattice QCD using the quenched approximation, where the dynamical quark-anitiquark pair creation is absent and no mixing occurs between the three-quark and the five-quark states. Our lattice QCD analysis suggests that the flavor-singlet three-quark state is so heavy that the $\Lambda$(1405) cannot be identified as the three-quark state, which supports the possibility of the molecular-state picture of the $\Lambda$(1405). Second, we study thermal properties of the scalar glueball in an anisotropic lattice QCD, and find about 300 MeV mass reduction near the QCD critical temperature from the pole-mass analysis. Finally, we study the three-quark potential, which is responsible to the baryon properties. The detailed lattice QCD analysis for the 3Q potential indicates the Y-type flux-tube formation linking the three quarks.

Thermal effects on the condensates of chiral order parameters, and g , and chiral restoration from lattice QCD

Abstract: We study the quark-gluon mixed condensate g q σ μη G μη q> using the SU(3)c lattice QCD with the Kogut-Susskind fermion at the quenched level. We perform the first but accurate measurement of the thermal effects on the mixed condensate in lattice QCD at β = 6.0 with 163 × Nt(Nt = 16, 12, 10, 8, 6, 4), β = 6.1 with 203 × Nt(Nt = 20, 12, 10, 8, 6), and β = 6.2 and with 243 × Nt(Nt = 24, 16, 12, 10, 8). At each temperature, the lattice calculation is carried out with high statistics using more than 100 gauge configurations. In particular, about 1000 gauge configurations are used near the critical temperature Tc. The chiral extrapolition is done from the lattice result with the current-quark mass of mq = 21, 36, 52MeV. While the thermal effects on both of g q σ μη G μη q> and q q> are very weak except for the vicinity of Tc, both the condensates suddenly vanish around Tc ∼ 280MeV, which indicates strong chiral restoratin near Tc. To compare the thermal effects on the two condensates, we analyze the ratio m 0 2 ≡g q σ μη G μη q>/ q q> , and find that m02 is almost independent of the temperature, even in the very vicinity of Tc. This means that these two different condensates obey the same critical behavior, and this nontrivial similarity between them would impose constraints on the chiral structure of the QCD vacuum near fc.

The lattice QCD simulation of the quark-gluon mixed condensate g at finite temperature and the phase transition of QCD

Abstract: The thermal effects on the quark-gluon mixed condensate g , which is another chiral order parameter, are studied using the SU(3)c lattice QCD with the Kogut-Susskind fermion at the quenched level. We perform the accurate measurement of the mixed condensate as well as the quark condensate for 0MeV / is almost independent of the temperature even in the very vicinity of T_c, which indicates that the two condensates have nontrivial similarity in the chiral behaviors. We also present the correlation between the condensates and the Polyakov loop to understand the vacuum structure of QCD.